Oral contraceptives and exercise.

A laboratory study was undertaken with volunteer females (aged 20-25) to determine the effect of OCs (oral contraceptives) on hematologic and metabolic variables during exercise. 5 of the women studied were naturally cycling and 7 were taking OCs. The women worked at 2 workloads on a bicycle ergometer at 50% and 90% of their maximal aerobic capacity during 3 different phases of their menstrual cycle. There was no better time of the month for doing the 50% or the 90% workload in either group. Heartrate for the OC group was significantly higher at the 50% maximal capacity. Results of the test indicate tha women on OCs have somewhat reduced cardiac efficiency and are ventilating more to carry out a given amount of work when compared to women who are naturally cycling. Possible explanations for the higher heart rate are put forward. The main limitation of the study is that the subject numbers involved are small and the number of cycles studied is also small.